Centering or like punch



25, E949. s. G. YOUNG CENTERING 0R LIKE PUNCH Filed Dec. 6, 1946 Patented Jan. 25, 1949 CENTERING R LIKE PUNCH Sidney Geoflrey Young, London, England Application December 6, 1946, Serial No. 714,564 In Great Britain November 26, 1945 Section 1, Public Law 690. August s, 1946 Patent expires November 26, 1965 This invention relates to an improved construction of automatic percussion punch of the kind employed, e. g. by toolmakers in punching centering marks in workpieces prior to further tooling operations thereon.

In prior known centering punches, there has been provided a punch member slidably movable in a casing, such casing having a striker or piston member also movable therein against the action of a spring when the punch is pressed against the workpiece, means being provided within the cas ing whereby, as the downward pressure upon the punch is continued, the striker member or piston is released when the operating spring is fully stressed, to permit the striker to beimpelled by the spring against the inner end of the punch member to produce an impression upon the workpiece.

In the use of such prior known centering punches, it has been found that difficulty is experienced, while exerting, a continuous downward pressure upon the punch to compress its operating spring, in maintaining the point of the punch member in exact register with the point marked upon the workpiece where the desired impression is to be made, and in some cases where for example, the pressure exterted upon the punch is in a direction not exactly normal to the surface of the workpiece, the point of the punch member tends to slip and to be displaced from its correct position.

According to the present invention, the improved centering punch comprises a tubular casing, in one end of which is provided a punch member, so mounted as to be slidable within limits within the casing, a striker member slidably mounted within the casing, a compression spring within the casing in association with the striker member, detent means for holding the striker at one limit of its travel with its operating spring substantially fully stressed, and trigger means whereby the detent may be moved to release the striker, whereon the latter is impelled by its spring to strike the inner end of the punch member.

By means of this improved construction of centering punch the user is enabled to stress-the operating spring of the tool and maintain the same in its loaded position prior to bringing the point of the punch member into register with the mark upon the workpiece where it is desired to produce an impression. When the point of the punch member 'has been accurately registered with such mark, the user has only to release the detent by means of any suitable trigger member 2 Claims. (Cl. 164-1235) to cause the striker to be projected against the inner end of the punch member, it not being necessary for the user to exert any pressure upon the tool to stress the operating spring while the point of the punch is in position upon the workin the accompanying drawing. It is to be understood however that many other constructional embodiments can be made and many changes in details efiected without departing from the concept of the invention.

In the said drawing,Figure 1 is a central section through a spring-loaded centering punch according to the invention, and

Figures 2 and 3 are detail views of punch setting mechanism hereinafter more fully described.

As shown in the said drawing, the improved centering punch comprises a cylindrical casing having a bushing 2 secured in position within the casing at a point adjacent an end thereof. In the end of the casing remote from the fixed bushing 2 is mounted a sliding bushing 8 having a shoulder thereon engaging an inwardly extending flange 5 provided on the end of the casing I. Y

The outer end of the slidingbushing I is internally screw-threaded to receive one end of a punch nose 6, in a central bore of which is slidably movable the punch i. A flange 8 on the punch I engages a shoulder within the bushing.

3 to retain the punch in position, a recess or enlargernent 9 of the bore of bushing 3 permitting sliding movement of the punch I within the limits of such recess 9. The inner end of the punch 1 extends into a recess or enlarged part H of the bore of the bush 3 at its innerend when the flange 8 thereon engages the innerrace of the recess 9.

A striking member or hammer is slidably mounted within the casing I, the head ll'oi' such striking member being slidable within the recess II, and the shank or shaft I2 of such hammer being slidably guided within the fixed bushing 2.

A helical compression spring 13 surrounds the-- hammer shank i2, its ends engaging the bushing 2 and the striking head "I, a second helical compression spring It being mounted within the casing, its end engaging the fixed bushing 2 and the sliding bushing 3.

Adjacent the upper end of the shank I! of the striking member is formed an annular recess It, with which engage alternatively one of 3 two pawls i8, H of unequal length pivotally mounted in a housing 20 provided in a cap member l8 secured upon the upper end of the casing l by means of screw-threaded parts l8.

Passing through a central bore in the top of the cap member 18 is a trigger member 2|, on the inner end of which is formed a frusto-conical sleeve 22 the inner face of which is adapted to. engage the ends it and I1 of the pawls l6 and I! which are each pivotally mounted in the housing 20 intermediate of their ends. A tension spring 23 secured to the two pawls Ii and I1 between their operative ends and their pivotal points urges the operative ends of such pawls against the shank 12 of the striking member when the latter is moved upwardly within the casing 1 against the compression spring 1!.

The operation of the improved punch is as follows: The point of the punch 1 is pressed against a hard surface, and the sliding bushing 3 slides upwardly in the casing, moving the striking member I 0, I2 upwardly against the action of the compression springs f3, ll until the inner end of the shank I2 protrudes beyond the upper end of the fixed bushing 2.

The annular recess l5 in the shank I2 is now engaged by the operative end of the longer pawl l7 and the striking member is thereby held against outward movement, the spring l3 being stressed. The pressure on the point of the punch 1 is now released, and the spring it returns the sliding bushing 3, the punch nose 6, and the punch I to the position shown in Figure 1 of the drawing.

The point of the punch I is then placed on the centering point marked on the workpiece, and the trigger 2| is pressed, the inner face of the conical sleeve 22 engaging the upper end of the pawl l1 and moving such end inwardly against the tension spring 23. The pawl is thus rocked on its pivot and its operative end is withdrawn from the recess i5, whereon the spring l3 returns the striking member l0, [2 with a hammer blow against the end of the punch I, which projects into the recess H in which the hammer head I0 is guided, thus making the desired impression upon the workpiece.

The operation of the punch as above described is intended for use when the material in which the impression is to be made is relatively soft. When such material is relatively hard, a more violent blow is required upon the punch I, and for this purpose, the shank I2 of the striking member is pressed further upwardly within the casing l, until the recess l5 therein is engaged by the operative end of the shorter pawl l6, thus stressing the spring l3 to a higher degree and enabling a blow of greater momentum to be imparted by the hammer III to the punch 1 when the trigger 2| is pressed to withdraw the pawl l8 from the recess I5 and release the stressed spring II.

To enable the user to pre-select the strength of hammer blow required in a given instance, means are provided in association with the trigger members 2!, 22 whereby the punch may be set to stress the spring l3 to give either a relatively light or a relatively heavy blow, by positively restraining the pawl It or the pawl l'l respectively from engaging in the recess IS in the shank l2 of thestriking member.

Such means comprise a cam surface 21 formed on the inner face of the conical member 22, and an indexing disc 24 fast upon the outer end of the trigger 2 i.

The indexing disc 24 is rotatable to bring one of two radial lines 25 thereon into register with a datum mark 26 on the top of the cap member i8, whereby the conical member 22 is similarly rotated to bring the cam surface on its inner face into engagement with the upper end of one of the pawls l6, l1 and moving such end inwardly to rock the pawl on its pivot and hold its operative end withdrawn from the position where it can engage in the recess l5 of the shank I2. The upper end of the other pawl is however not engaged by the cam surface on the member 22 and its lower or operative end is thus free to be drawn by the spring 23 into engagement with the recess I! in the shank l2 of the striking member when the spring i3 is stressed to the necessary extent.

' Iclaim:

' 1. A centering punch comprising a tubular casing, a bushing slidably mounted in'one end of such casing, a punch member mounted so as to be slidably movable within limits within such bushing, abutments to limit the slidable movement of such bushing, a striker member, slidably mounted within the casing, a compression spring within the casing in association with the said striker member, detent means for holding the striker member in a position in which its associ ated compression spring is stressed, and trigger means whereby the detent means may be moved to release the striking member for movement by its associated spring to impart a blow to the punch member.

2. A centering punch comprising a tubular casing, a punch member mounted in one end of such casing so as to slidably move therein, abutments to limit the slidable movement of such punch, a striker member slidably mounted within the casing, a compression spring within the casing in association with the said striker member,detent means whereby the striker member may be held in one of a number of positions in which its associated compression spring is stressed to an equivalent number of degrees of tension, trigger means whereby the detent means may be moved to release the striking member for movement by its associated spring to impart a blow to the punch member, and indexing means in association with the trigger means whereby the detent means may be selectively engaged to hold the striker member with its associated spring stressed The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 797,824 Seitz Aug. 22, 1905 Ainsworth Mar. 2, 1909 Certificate of Correction Patent No. 2,460,113. January 25, 1949.

v SIDNEY GEOFFREY YOUNG It is hereby certified that errors appear in the above numbered patent requiring correction as follows: 7 I

. In the grant, lines 14 and 15, strike out the words for the term from the date of this grant until November 26, 1965 and insert instead for the term of seventeen years from the date of this grant; in the heading to the printed specification, line 6, strike out Section 1, Public Law 690, August 8; 1946; line 7, strike out Patent expires November 26, 1965";

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 8th day of March, A. D. 1949.

THOMAS F. MURPHY,

Assistant Uommissimer of Patents. 

